I advise everyone not to use Cr12MoV for stretching molds with coatings, as there are few successful ones. Although the price of Cr12MoV is very cheap, you will lose big for small gains. What you are losing is not only the tool steel, but also dozens of dollars per kilogram for coating costs, mold processing costs, and a series of problems caused by the inability to mass produce the mold.
In my 285th live broadcast, a netizen came to ask, “What is a good solution to solve the problem of wire drawing when forming 5mm Q340 iron material and using Cr12MoV+TD processing for the mold?
To be honest, there’s no way to solve it. This is caused by using the wrong substrate.
All wire drawing is caused by adhesive wear of the adhesive material, and the root cause of adhesive wear of the adhesive material is that the uniformity of the steel structure of your mold is too poor, with a large number of microscopic and fine cracks that cannot be seen by the naked eye. When forming and contacting the parts, the cracks adhere to the parts, resulting in a series of problems such as wire drawing and scratching of the product.
Coating is a chemical heat treatment that infiltrates atoms into the surface of the metal to improve its wear resistance and surface smoothness. However, if the substrate has too many and too large cracks, the coating cannot cover it, and the coating will not be effective, resulting in adhesive wear of the adhesive and the problem of wire drawing.
Using Cr12MoV as the base layer for coating is already a mistake. The reason is that Cr12MoV is a high carbon steel with a carbon content of 1.5%. The material segregation of high carbon steel is very serious, and there are many fine cracks. Even if it is coated, it cannot cover it. During the mold production process, tensile marks will appear, and you cannot produce many products. Even if you use SKD11, it is useless.
Due to the extremely low price of Cr12MoV nowadays, the smelting quality is extremely poor, and segregation is even more severe. Therefore, using Cr12MoV as a substrate for coating is a waste of money, and not only is Cr12MoV itself wasted, but also the coating cost of tens of yuan per kilogram, and the mold is also wasted. In the future, don’t foolishly think that choosing cheaper tool steel for coating can reduce costs. This is not about reducing costs, but about finding a reason to spend more money and paying for your ignorance.
We have a customer who stretches 1.2mm thick stainless steel. The mold is over 1 meter long and has been treated with SKD11+TD. However, there are scratches on the mold when making 500 products. What is the material cost for a mold that is over 1 meter long. Moreover, the TD processing fee is said to be 70 yuan per kilogram, which is much more expensive than the coating cost of SKH51 high-speed steel. A mold that is over 1 meter long requires a certain amount of tool steel. However, after pulling 500 products, scratches appear, coatings are wasted, tool steel is wasted, the mold is made in vain, and the goods cannot be delivered. Isn’t this a case of losing big for small gains.
The mold for coating must meet three performance requirements: high strength and hardness of around 60HRC; Good toughness, ensuring that the mold does not crack during use; Good organizational uniformity, few minor cracks, easy coating, and tempering temperature above 520 ℃ to avoid poor coating effect and decreased substrate hardness, wasting high coating costs. If your mold needs to be coated, I recommend three types of tool steel.
The first type is non stick 8503 die steel. 8503 is a non stick tool steel exclusive to Yuhui Tool Steel. Its hardness is 59-61HRC, and its toughness is twice that of DC53. Compared with DC53, its performance doubles, its price does not double, and it also has the advantage of non stick material. The advantage of this non stick material is that it has good smelting quality and no microscopic cracks that are invisible to the naked eye.
The coating meets all three performance requirements for tool steel, and 8503 fully satisfies them. Using non stick 8503 for coating can achieve twice the result with half the effort. Some stretching molds use 8503 and even do not require coating.
The second one is wear-resistant steel 6077，6077with a hardness of 60-63HRC and toughness three times that of Cr12MoV. The tempering temperature is 530 ℃, and the performance meets the coating requirements. There have been successful cases of stretching molds.
Mr. Tan stretched the motor casing of 0.7mm thick galvanized sheet to a height of 30mm using wear-resistant steel 6077. The mold was made 3 million times and was not scrapped. Previously, when using DC53, it would start drawing after not being able to produce many products, which was criticized by customers to death. I am glad that the customer no longer complains or curses.
Thirdly, if you really don’t want to use non stick 8503 and wear-resistant steel 6077, I recommend using Cr8 series cold work die steel, which has a carbon content of 1.0% lower than Cr12MoV, less severe segregation, and can be covered by the coating. The Cr8 series of cold work die steels have grades such as PD613, ASSAB 88, K340, SLD-MAGIC, DC53, etc. The key is that the forging should be sufficient. After six sided forging, three forging and three pulling, the segregation is not as severe as Cr12MoV, SKD11, D2, and Cr12 type cold work die steel with a carbon content of 1.5%. The coating can cover it and the effect will be better.
Just a reminder, don’t say that the price of this type of material is higher than your Cr12MoV. Your Cr12MoV is cheap, but useless. Coating with Cr12MoV is a waste of money. Even if you have a coating, it cannot cover it, and the mold cannot produce many products before drawing. The cost of coating several tens of yuan per kilogram is wasted. Cr12MoV is just a waste, and the mold is useless. People are tired of it, and they can’t deliver the goods. Even if the mold is cheap, it is a burden.
The netizen said that the formed 5mm Q340 iron material, treated with Cr12MoV+TD, can start drawing after not drying many products. This cannot be solved, you can only change the material, there is no other way. Even if you go back to the furnace to melt Cr12MoV again, it will be useless. You can switch to the tool steels I recommended above. Prioritize non stick material 8503, then use wear-resistant steel 6077, and finally use Cr8 series cold work die steel, combined with coating, to solve the problem of wire drawing in your current mold. The coating at this time is the icing on the cake. Choosing the wrong mold steel is a waste of effort.